Mention in new editor does not work well with macOS input method
I have to say it might be hard to understand this issue, if you don't use input method to type non-English characters.
I have only tested this in macOS, not sure about Windows.
With system's input method enabled, after typing "@" in editor, the following letter I typed would not be recognized by input method, but just typed as an English letter, thus I cannot type the character I want through it. If I keep typing letters, the next letter can trigger input method. But since the first letter is missing, I am still unable to type the character.
For example, I'm personally using system's Chinese input method, and let's say we need the Pinyin input method to convert letters "wo" into Chinese character "我", and we would like to mention it as "@我". So I try to type "@wo", which is supposed to be converted to "@我" with input method. However, since first letter after @ can't be recognized by input method, "@w" is typed directly into the editor, and then "o" goes into input method change being converted to another character I don't want as "@w哦".